1
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Sun J, Zhang C, Gao F, Stathopoulos A. Single-cell transcriptomics illuminates regulatory steps driving anterior-posterior patterning of Drosophila embryonic mesoderm. Cell Rep 2023; 42:113289. [PMID: 37858470 DOI: 10.1016/j.celrep.2023.113289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 08/29/2023] [Accepted: 09/29/2023] [Indexed: 10/21/2023] Open
Abstract
Single-cell technologies promise to uncover how transcriptional programs orchestrate complex processes during embryogenesis. Here, we apply a combination of single-cell technology and genetic analysis to investigate the dynamic transcriptional changes associated with Drosophila embryo morphogenesis at gastrulation. Our dataset encompassing the blastoderm-to-gastrula transition provides a comprehensive single-cell map of gene expression across cell lineages validated by genetic analysis. Subclustering and trajectory analyses revealed a surprising stepwise progression in patterning to transition zygotic gene expression and specify germ layers as well as uncovered an early role for ecdysone signaling in epithelial-to-mesenchymal transition in the mesoderm. We also show multipotent progenitors arise prior to gastrulation by analyzing the transcription trajectory of caudal mesoderm cells, including a derivative that ultimately incorporates into visceral muscles of the midgut and hindgut. This study provides a rich resource of gastrulation and elucidates spatially regulated temporal transitions of transcription states during the process.
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Affiliation(s)
- Jingjing Sun
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Chen Zhang
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Fan Gao
- Bioinformatics Resource Center, Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA
| | - Angelike Stathopoulos
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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2
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Brückner DB, Chen H, Barinov L, Zoller B, Gregor T. Stochastic motion and transcriptional dynamics of pairs of distal DNA loci on a compacted chromosome. Science 2023; 380:1357-1362. [PMID: 37384691 PMCID: PMC10439308 DOI: 10.1126/science.adf5568] [Citation(s) in RCA: 22] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Accepted: 05/31/2023] [Indexed: 07/01/2023]
Abstract
Chromosomes in the eukaryotic nucleus are highly compacted. However, for many functional processes, including transcription initiation, the pairwise motion of distal chromosomal elements such as enhancers and promoters is essential and necessitates dynamic fluidity. Here, we used a live-imaging assay to simultaneously measure the positions of pairs of enhancers and promoters and their transcriptional output while systematically varying the genomic separation between these two DNA loci. Our analysis reveals the coexistence of a compact globular organization and fast subdiffusive dynamics. These combined features cause an anomalous scaling of polymer relaxation times with genomic separation leading to long-ranged correlations. Thus, encounter times of DNA loci are much less dependent on genomic distance than predicted by existing polymer models, with potential consequences for eukaryotic gene expression.
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Affiliation(s)
- David B. Brückner
- Institute of Science and Technology, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Hongtao Chen
- School of Life Science and Technology, ShanghaiTech University, Shanghai, China
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA
| | - Lev Barinov
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA
- Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Benjamin Zoller
- Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ, USA
- Department of Developmental and Stem Cell Biology, CNRS UMR3738 Paris Cité, Institut Pasteur, Paris, France
| | - Thomas Gregor
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA
- Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ, USA
- Department of Developmental and Stem Cell Biology, CNRS UMR3738 Paris Cité, Institut Pasteur, Paris, France
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3
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Fenelon KD, Gao F, Borad P, Abbasi S, Pachter L, Koromila T. Cell-specific occupancy dynamics between the pioneer-like factor Opa/ZIC and Ocelliless/OTX regulate early head development in embryos. Front Cell Dev Biol 2023; 11:1126507. [PMID: 37051467 PMCID: PMC10083704 DOI: 10.3389/fcell.2023.1126507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Accepted: 03/16/2023] [Indexed: 03/29/2023] Open
Abstract
During development, embryonic patterning systems direct a set of initially uncommitted pluripotent cells to differentiate into a variety of cell types and tissues. A core network of transcription factors, such as Zelda/POU5F1, Odd-paired (Opa)/ZIC3 and Ocelliless (Oc)/OTX2, are conserved across animals. While Opa is essential for a second wave of zygotic activation after Zelda, it is unclear whether Opa drives head cell specification, in the Drosophila embryo. Our hypothesis is that Opa and Oc are interacting with distinct cis-regulatory regions for shaping cell fates in the embryonic head. Super-resolution microscopy and meta-analysis of single-cell RNAseq datasets show that opa’s and oc’s overlapping expression domains are dynamic in the head region, with both factors being simultaneously transcribed at the blastula stage. Additionally, analysis of single-embryo RNAseq data reveals a subgroup of Opa-bound genes to be Opa-independent in the cellularized embryo. Interrogation of these genes against Oc ChIPseq combined with in situ data, suggests that Opa is competing with Oc for the regulation of a subgroup of genes later in gastrulation. Specifically, we find that Oc binds to late, head-specific enhancers independently and activates them in a head-specific wave of zygotic transcription, suggesting distinct roles for Oc in the blastula and gastrula stages.
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Affiliation(s)
- Kelli D. Fenelon
- Department of Biology, UT Arlington, Arlington, TX, United States
| | - Fan Gao
- Caltech Bioinformatics Resource Center (CBRC), Caltech, Pasadena, CA, United States
| | - Priyanshi Borad
- Department of Biology, UT Arlington, Arlington, TX, United States
| | - Shiva Abbasi
- Department of Biology, UT Arlington, Arlington, TX, United States
| | - Lior Pachter
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States
- Department of Computational Biology and Computing and Mathematical Sciences, California Institute of Technology, Pasadena, CA, United States
| | - Theodora Koromila
- Department of Biology, UT Arlington, Arlington, TX, United States
- *Correspondence: Theodora Koromila,
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4
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Li M, Kasan K, Saha Z, Yoon Y, Schmidt-Ott U. Twenty-seven ZAD-ZNF genes of Drosophila melanogaster are orthologous to the embryo polarity determining mosquito gene cucoid. PLoS One 2023; 18:e0274716. [PMID: 36595500 PMCID: PMC9810180 DOI: 10.1371/journal.pone.0274716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 12/16/2022] [Indexed: 01/04/2023] Open
Abstract
The C2H2 zinc finger gene cucoid establishes anterior-posterior (AP) polarity in the early embryo of culicine mosquitoes. This gene is unrelated to genes that establish embryo polarity in other fly species (Diptera), such as the homeobox gene bicoid, which serves this function in the traditional model organism Drosophila melanogaster. The cucoid gene is a conserved single copy gene across lower dipterans but nothing is known about its function in other species, and its evolution in higher dipterans, including Drosophila, is unresolved. We found that cucoid is a member of the ZAD-containing C2H2 zinc finger (ZAD-ZNF) gene family and is orthologous to 27 of the 91 members of this family in D. melanogaster, including M1BP, ranshi, ouib, nom, zaf1, odj, Nnk, trem, Zif, and eighteen uncharacterized genes. Available knowledge of the functions of cucoid orthologs in Drosophila melanogaster suggest that the progenitor of this lineage specific expansion may have played a role in regulating chromatin. We also describe many aspects of the gene duplication history of cucoid in the brachyceran lineage of D. melanogaster, thereby providing a framework for predicting potential redundancies among these genes in D. melanogaster.
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Affiliation(s)
- Muzi Li
- Dept. of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, United States of America
| | - Koray Kasan
- Dept. of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, United States of America
| | - Zinnia Saha
- Dept. of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, United States of America
| | - Yoseop Yoon
- Dept. of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, United States of America
| | - Urs Schmidt-Ott
- Dept. of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, United States of America
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5
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Datta RR, Onal P. In Situ Hybridization as a Method to Examine Gene Regulatory Activity In Vivo. Methods Mol Biol 2023; 2599:241-254. [PMID: 36427154 DOI: 10.1007/978-1-0716-2847-8_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Transcription factor-enhancer binding events are among the most well-studied protein-DNA interactions, allowing researchers to determine mechanisms of transcriptional activation or repression during development. While large-scale ChIP-sequence datasets, together with computational predictions and chromatin accessibility data, yield information on potential transcription factor binding activities, reporter gene assays provide measurable information on whether these binding activities are functional in particular cell types during development. Here, we present a detailed protocol to examine enhancer activity in Drosophila embryos using cloning, transgenesis, and in situ hybridization.
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Affiliation(s)
- Rhea R Datta
- Department of Biology, Hamilton College, Clinton, NY, USA.
| | - Pinar Onal
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, USA.
- Department of Molecular Biology and Genetics, Ihsan Dogramaci Bilkent University, Ankara, Turkey.
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6
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Kim YJ, Rhee K, Liu J, Jeammet S, Turner MA, Small SJ, Garcia HG. Predictive modeling reveals that higher-order cooperativity drives transcriptional repression in a synthetic developmental enhancer. eLife 2022; 11:73395. [PMID: 36503705 PMCID: PMC9836395 DOI: 10.7554/elife.73395] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 12/09/2022] [Indexed: 12/14/2022] Open
Abstract
A challenge in quantitative biology is to predict output patterns of gene expression from knowledge of input transcription factor patterns and from the arrangement of binding sites for these transcription factors on regulatory DNA. We tested whether widespread thermodynamic models could be used to infer parameters describing simple regulatory architectures that inform parameter-free predictions of more complex enhancers in the context of transcriptional repression by Runt in the early fruit fly embryo. By modulating the number and placement of Runt binding sites within an enhancer, and quantifying the resulting transcriptional activity using live imaging, we discovered that thermodynamic models call for higher-order cooperativity between multiple molecular players. This higher-order cooperativity captures the combinatorial complexity underlying eukaryotic transcriptional regulation and cannot be determined from simpler regulatory architectures, highlighting the challenges in reaching a predictive understanding of transcriptional regulation in eukaryotes and calling for approaches that quantitatively dissect their molecular nature.
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Affiliation(s)
- Yang Joon Kim
- Chan Zuckerberg Biohub, San Francisco, United States
| | - Kaitlin Rhee
- Department of Chemical Biology, University of California, Berkeley, Berkeley, United States
| | - Jonathan Liu
- Department of Physics, University of California, Berkeley, Berkeley, United States
| | - Selene Jeammet
- Department of Biology, Ecole Polytechnique, Paris, France
| | - Meghan A Turner
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
| | - Stephen J Small
- Department of Biology, New York University, New York, United States
| | - Hernan G Garcia
- Chan Zuckerberg Biohub, San Francisco, United States.,Department of Physics, University of California, Berkeley, Berkeley, United States.,Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States.,Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Institute for Quantitative Biosciences-QB3, University of California at Berkeley, Berkeley, United States
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7
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Abstract
Metazoan embryos develop from a single cell into three-dimensional structured organisms while groups of genetically identical cells attain specialized identities. Cells of the developing embryo both create and accurately interpret morphogen gradients to determine their positions and make specific decisions in response. Here, we first cover intellectual roots of morphogen and positional information concepts. Focusing on animal embryos, we then provide a review of current understanding on how morphogen gradients are established and how their spans are controlled. Lastly, we cover how gradients evolve in time and space during development, and how they encode information to control patterning. In sum, we provide a list of patterning principles for morphogen gradients and review recent advances in quantitative methodologies elucidating information provided by morphogens.
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Affiliation(s)
- M. Fethullah Simsek
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA
| | - Ertuğrul M. Özbudak
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA,Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA
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8
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Vuilleumier R, Miao M, Medina-Giro S, Ell CM, Flibotte S, Lian T, Kauwe G, Collins A, Ly S, Pyrowolakis G, Haghighi A, Allan D. Dichotomous cis-regulatory motifs mediate the maturation of the neuromuscular junction by retrograde BMP signaling. Nucleic Acids Res 2022; 50:9748-9764. [PMID: 36029115 PMCID: PMC9508838 DOI: 10.1093/nar/gkac730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Revised: 07/20/2022] [Accepted: 08/19/2022] [Indexed: 11/26/2022] Open
Abstract
Retrograde bone morphogenetic protein (BMP) signaling at the Drosophila neuromuscular junction (NMJ) has served as a paradigm to study TGF-β-dependent synaptic function and maturation. Yet, how retrograde BMP signaling transcriptionally regulates these functions remains unresolved. Here, we uncover a gene network, enriched for neurotransmission-related genes, that is controlled by retrograde BMP signaling in motor neurons through two Smad-binding cis-regulatory motifs, the BMP-activating (BMP-AE) and silencer (BMP-SE) elements. Unpredictably, both motifs mediate direct gene activation, with no involvement of the BMP derepression pathway regulators Schnurri and Brinker. Genome editing of candidate BMP-SE and BMP-AE within the locus of the active zone gene bruchpilot, and a novel Ly6 gene witty, demonstrated the role of these motifs in upregulating genes required for the maturation of pre- and post-synaptic NMJ compartments. Our findings uncover how Smad-dependent transcriptional mechanisms specific to motor neurons directly orchestrate a gene network required for synaptic maturation by retrograde BMP signaling.
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Affiliation(s)
- Robin Vuilleumier
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
| | - Mo Miao
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
| | - Sonia Medina-Giro
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
| | - Clara-Maria Ell
- Spemann Graduate School of Biology and Medicine (SGBM), University of Freiburg, Freiburg, 79104, Germany
- CIBSS - Centre for Integrative Biological Signaling Studies and Institute for Biology I, Faculty of Biology, Hilde Mangold Haus, Habsburgerstrasse 49, University of Freiburg, Freiburg, 79104, Germany
| | - Stephane Flibotte
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
| | - Tianshun Lian
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
| | - Grant Kauwe
- Buck Institute for Research on Aging, Novato, CA 94945, USA
| | - Annie Collins
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
| | - Sophia Ly
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
| | - George Pyrowolakis
- CIBSS - Centre for Integrative Biological Signaling Studies and Institute for Biology I, Faculty of Biology, Hilde Mangold Haus, Habsburgerstrasse 49, University of Freiburg, Freiburg, 79104, Germany
| | | | - Douglas W Allan
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
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9
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Wang Z, Pan N, Yan J, Wan J, Wan C. Systematic Identification of Microproteins during the Development of Drosophila melanogaster. J Proteome Res 2022; 21:1114-1123. [PMID: 35227063 DOI: 10.1021/acs.jproteome.2c00004] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Short open reading frame-encoded peptides (SEPs) are microproteins with less than 100 amino acids that play an essential role in the growth and development of organisms. There are plenty of short open reading frames in Drosophila melanogaster that potentially code polypeptides. We chose 11 time points during the life cycle of Drosophila to investigate microproteins, particularly those related to development. Finally, we identified a total of 410 microproteins, of which 27 were noncoding RNA-encoded proteins. Of the 410 microproteins, 74 were expressed in all stages from embryo to adults, whereas 300 microproteins were only found in one or two time points. Approximately, one-third of the microproteins were not reported previously and 44 were obtained from de novo sequencing, validated by synthetic peptides. These microproteins are related to the main bioprocesses of growth and development, such as multicellular organism reproduction, postmating behavior, and oviposition. Over half of the microproteins have predicted functional domains and are conserved across species, suggesting that these microproteins have critical functions in fly development. This work enriches the D. melanogaster proteome and provides a significant data resource for growth and development research.
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Affiliation(s)
- Zhiwei Wang
- School of Life Sciences and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, Hubei 430079, People's Republic of China
| | - Ni Pan
- School of Life Sciences and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, Hubei 430079, People's Republic of China
| | - Jiahao Yan
- School of Life Sciences and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, Hubei 430079, People's Republic of China
| | - Jian Wan
- School of Life Sciences and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, Hubei 430079, People's Republic of China
| | - Cuihong Wan
- School of Life Sciences and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, Hubei 430079, People's Republic of China
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10
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Tsai A, Crocker J. Nuclear morphogenesis: forming a heterogeneous nucleus during embryogenesis. Development 2022; 149:274325. [PMID: 35142344 PMCID: PMC8918797 DOI: 10.1242/dev.200266] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 01/18/2022] [Indexed: 11/20/2022]
Abstract
ABSTRACT
An embryo experiences increasingly complex spatial and temporal patterns of gene expression as it matures, guiding the morphogenesis of its body. Using super-resolution fluorescence microscopy in Drosophila melanogaster embryos, we observed that the nuclear distributions of transcription factors and histone modifications undergo a similar transformation of increasing heterogeneity. This spatial partitioning of the nucleus could lead to distinct local regulatory environments in space and time that are tuned for specific genes. Accordingly, transcription sites driven by different cis-regulatory regions each had their own temporally and spatially varying local histone environments, which could facilitate the finer spatial and temporal regulation of genes to consistently differentiate cells into organs and tissues. Thus, ‘nuclear morphogenesis’ may be a microscopic counterpart of the macroscopic process that shapes the animal body.
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Affiliation(s)
- Albert Tsai
- European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - Justin Crocker
- European Molecular Biology Laboratory, 69117 Heidelberg, Germany
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11
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Waymack R, Gad M, Wunderlich Z. Molecular competition can shape enhancer activity in the Drosophila embryo. iScience 2021; 24:103034. [PMID: 34568782 PMCID: PMC8449247 DOI: 10.1016/j.isci.2021.103034] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 07/27/2021] [Accepted: 08/20/2021] [Indexed: 01/12/2023] Open
Abstract
Transgenic reporters allow the measurement of regulatory DNA activity in vivo and consequently have long been useful tools for studying enhancers. Despite their utility, few studies have investigated the effects these reporters may have on the expression of other genes. Understanding these effects is required to accurately interpret reporter data and characterize gene regulatory mechanisms. By measuring the expression of Kruppel (Kr) enhancer reporters in live Drosophila embryos, we find reporters inhibit one another's expression and that of a nearby endogenous gene. Using synthetic transcription factor (TF) binding site arrays, we present evidence that competition for TFs is partially responsible for the observed transcriptional inhibition. We develop a simple thermodynamic model that predicts competition of the measured magnitude specifically when TF binding is restricted to distinct nuclear subregions. Our findings underline an unexpected role of the non-homogenous nature of the nucleus in regulating gene expression.
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Affiliation(s)
- Rachel Waymack
- Department of Developmental and Cell Biology, University of California, Irvine, CA 92697, USA
| | - Mario Gad
- Department of Developmental and Cell Biology, University of California, Irvine, CA 92697, USA
| | - Zeba Wunderlich
- Department of Developmental and Cell Biology, University of California, Irvine, CA 92697, USA
- Department of Biology, Boston University, 610 Commonwealth Ave., Boston, MA 02215, USA
- Biological Design Center, Boston University, 610 Commonwealth Avenue, Boston, MA 02215, USA
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12
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Onal P, Gunasinghe HI, Umezawa KY, Zheng M, Ling J, Azeez L, Dalmeus A, Tazin T, Small S. Suboptimal Intermediates Underlie Evolution of the Bicoid Homeodomain. Mol Biol Evol 2021; 38:2179-2190. [PMID: 33599280 PMCID: PMC8136501 DOI: 10.1093/molbev/msab051] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Changes in regulatory networks generate materials for evolution to create phenotypic diversity. For transcription networks, multiple studies have shown that alterations in binding sites of cis-regulatory elements correlate well with the gain or loss of specific features of the body plan. Less is known about alterations in the amino acid sequences of the transcription factors (TFs) that bind these elements. Here we study the evolution of Bicoid (Bcd), a homeodomain (HD) protein that is critical for anterior embryo patterning in Drosophila. The ancestor of Bcd (AncBcd) emerged after a duplication of a Zerknullt (Zen)-like ancestral protein (AncZB) in a suborder of flies. AncBcd diverged from AncZB, gaining novel transcriptional and translational activities. We focus on the evolution of the HD of AncBcd, which binds to DNA and RNA, and is comprised of four subdomains: an N-terminal arm (NT) and three helices; H1, H2, and Recognition Helix (RH). Using chimeras of subdomains and gene rescue assays in Drosophila, we show that robust patterning activity of the Bcd HD (high frequency rescue to adulthood) is achieved only when amino acid substitutions in three separate subdomains (NT, H1, and RH) are combined. Other combinations of subdomains also yield full rescue, but with lower penetrance, suggesting alternative suboptimal activities. Our results suggest a multistep pathway for the evolution of the Bcd HD that involved intermediate HD sequences with suboptimal activities, which constrained and enabled further evolutionary changes. They also demonstrate critical epistatic forces that contribute to the robust function of a DNA-binding domain.
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Affiliation(s)
- Pinar Onal
- Department of Biology, New York University, New York, NY, USA
| | | | | | - Michael Zheng
- Department of Biology, New York University, New York, NY, USA
| | - Jia Ling
- Department of Biology, New York University, New York, NY, USA
| | - Leen Azeez
- Department of Biology, New York University, New York, NY, USA
| | - Anecine Dalmeus
- Department of Biology, New York University, New York, NY, USA
| | - Tasmima Tazin
- Department of Biology, New York University, New York, NY, USA
| | - Stephen Small
- Department of Biology, New York University, New York, NY, USA
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13
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Abstract
Arthropod segmentation and vertebrate somitogenesis are leading fields in the experimental and theoretical interrogation of developmental patterning. However, despite the sophistication of current research, basic conceptual issues remain unresolved. These include: (i) the mechanistic origins of spatial organization within the segment addition zone (SAZ); (ii) the mechanistic origins of segment polarization; (iii) the mechanistic origins of axial variation; and (iv) the evolutionary origins of simultaneous patterning. Here, I explore these problems using coarse-grained models of cross-regulating dynamical processes. In the morphogenetic framework of a row of cells undergoing axial elongation, I simulate interactions between an 'oscillator', a 'switch' and up to three 'timers', successfully reproducing essential patterning behaviours of segmenting systems. By comparing the output of these largely cell-autonomous models to variants that incorporate positional information, I find that scaling relationships, wave patterns and patterning dynamics all depend on whether the SAZ is regulated by temporal or spatial information. I also identify three mechanisms for polarizing oscillator output, all of which functionally implicate the oscillator frequency profile. Finally, I demonstrate significant dynamical and regulatory continuity between sequential and simultaneous modes of segmentation. I discuss these results in the context of the experimental literature.
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Affiliation(s)
- Erik Clark
- Department of Systems Biology, Harvard Medical School, 210 Longwood Ave, Boston, MA 02115, USA
- Trinity College Cambridge, University of Cambridge, Trinity Street, Cambridge CB2 1TQ, UK
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14
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Liu J, Hansen D, Eck E, Kim YJ, Turner M, Alamos S, Garcia HG. Real-time single-cell characterization of the eukaryotic transcription cycle reveals correlations between RNA initiation, elongation, and cleavage. PLoS Comput Biol 2021; 17:e1008999. [PMID: 34003867 PMCID: PMC8162642 DOI: 10.1371/journal.pcbi.1008999] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 05/28/2021] [Accepted: 04/23/2021] [Indexed: 12/23/2022] Open
Abstract
The eukaryotic transcription cycle consists of three main steps: initiation, elongation, and cleavage of the nascent RNA transcript. Although each of these steps can be regulated as well as coupled with each other, their in vivo dissection has remained challenging because available experimental readouts lack sufficient spatiotemporal resolution to separate the contributions from each of these steps. Here, we describe a novel application of Bayesian inference techniques to simultaneously infer the effective parameters of the transcription cycle in real time and at the single-cell level using a two-color MS2/PP7 reporter gene and the developing fruit fly embryo as a case study. Our method enables detailed investigations into cell-to-cell variability in transcription-cycle parameters as well as single-cell correlations between these parameters. These measurements, combined with theoretical modeling, suggest a substantial variability in the elongation rate of individual RNA polymerase molecules. We further illustrate the power of this technique by uncovering a novel mechanistic connection between RNA polymerase density and nascent RNA cleavage efficiency. Thus, our approach makes it possible to shed light on the regulatory mechanisms in play during each step of the transcription cycle in individual, living cells at high spatiotemporal resolution.
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Affiliation(s)
- Jonathan Liu
- Department of Physics, University of California at Berkeley, Berkeley, California, United States of America
| | - Donald Hansen
- Institute of Pharmacy and Molecular Biotechnology, University of Heidelberg, Heidelberg, Germany
| | - Elizabeth Eck
- Biophysics Graduate Group, University of California at Berkeley, Berkeley, California, United States of America
| | - Yang Joon Kim
- Biophysics Graduate Group, University of California at Berkeley, Berkeley, California, United States of America
| | - Meghan Turner
- Biophysics Graduate Group, University of California at Berkeley, Berkeley, California, United States of America
| | - Simon Alamos
- Department of Plant and Microbial Biology, University of California at Berkeley, Berkeley, California, United States of America
| | - Hernan G. Garcia
- Department of Physics, University of California at Berkeley, Berkeley, California, United States of America
- Biophysics Graduate Group, University of California at Berkeley, Berkeley, California, United States of America
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California, United States of America
- Institute for Quantitative Biosciences-QB3, University of California at Berkeley, Berkeley, California, United States of America
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15
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Cao Y, Neu J, Blanchard AE, Lu T, You L. Repulsive expansion dynamics in colony growth and gene expression. PLoS Comput Biol 2021; 17:e1008168. [PMID: 33735192 PMCID: PMC8009408 DOI: 10.1371/journal.pcbi.1008168] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 03/30/2021] [Accepted: 02/15/2021] [Indexed: 01/05/2023] Open
Abstract
Spatial expansion of a population of cells can arise from growth of microorganisms, plant cells, and mammalian cells. It underlies normal or dysfunctional tissue development, and it can be exploited as the foundation for programming spatial patterns. This expansion is often driven by continuous growth and division of cells within a colony, which in turn pushes the peripheral cells outward. This process generates a repulsion velocity field at each location within the colony. Here we show that this process can be approximated as coarse-grained repulsive-expansion kinetics. This framework enables accurate and efficient simulation of growth and gene expression dynamics in radially symmetric colonies with homogenous z-directional distribution. It is robust even if cells are not spherical and vary in size. The simplicity of the resulting mathematical framework also greatly facilitates generation of mechanistic insights. Spatiotemporal dynamics are ubiquitous in biology. To understand these phenomena in nature or to program them using synthetic gene circuits, it is critical to resort to mathematical modeling to deduce mechanistic insights or to explore plausible outcomes. Historically, modeling of spatiotemporal dynamics depends on the use of agent-based models or their continuum counterparts consisting of partial differential equations. Here, we show that a class of colony expansion can be treated as being driven by the steric force generated by growing and diving cells. This approximation leads to a drastically simplified framework consisting of only ordinary differential equations. This framework greatly improves the computational efficiency and facilitates development of mechanistic insights into the dynamics of colony growth and pattern formation.
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Affiliation(s)
- Yangxiaolu Cao
- Department of Biomedical Engineering, Duke University, Durham, North Carolina
| | - John Neu
- Department of Biomedical Engineering, Duke University, Durham, North Carolina
| | - Andrew E. Blanchard
- Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Ting Lu
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois
- Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Lingchong You
- Department of Biomedical Engineering, Duke University, Durham, North Carolina
- Center for Genomic and Computational Biology, Duke University, Durham, North Carolina
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina
- * E-mail:
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16
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Irizarry J, Stathopoulos A. Dynamic patterning by morphogens illuminated by cis-regulatory studies. Development 2021; 148:148/2/dev196113. [PMID: 33472851 DOI: 10.1242/dev.196113] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Morphogen concentration changes in space as well as over time during development. However, how these dynamics are interpreted by cells to specify fate is not well understood. Here, we focus on two morphogens: the maternal transcription factors Bicoid and Dorsal, which directly regulate target genes to pattern Drosophila embryos. The actions of these factors at enhancers has been thoroughly dissected and provides a rich platform for understanding direct input by morphogens and their changing roles over time. Importantly, Bicoid and Dorsal do not work alone; we also discuss additional inputs that work with morphogens to control spatiotemporal gene expression in embryos.
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Affiliation(s)
- Jihyun Irizarry
- California Institute of Technology, Division of Biology and Biological Engineering, 1200 East California Blvd., Pasadena, CA 91125, USA
| | - Angelike Stathopoulos
- California Institute of Technology, Division of Biology and Biological Engineering, 1200 East California Blvd., Pasadena, CA 91125, USA
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17
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Rogers KW, ElGamacy M, Jordan BM, Müller P. Optogenetic investigation of BMP target gene expression diversity. eLife 2020; 9:58641. [PMID: 33174840 PMCID: PMC7728441 DOI: 10.7554/elife.58641] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 11/10/2020] [Indexed: 12/15/2022] Open
Abstract
Signaling molecules activate distinct patterns of gene expression to coordinate embryogenesis, but how spatiotemporal expression diversity is generated is an open question. In zebrafish, a BMP signaling gradient patterns the dorsal-ventral axis. We systematically identified target genes responding to BMP and found that they have diverse spatiotemporal expression patterns. Transcriptional responses to optogenetically delivered high- and low-amplitude BMP signaling pulses indicate that spatiotemporal expression is not fully defined by different BMP signaling activation thresholds. Additionally, we observed negligible correlations between spatiotemporal expression and transcription kinetics for the majority of analyzed genes in response to BMP signaling pulses. In contrast, spatial differences between BMP target genes largely collapsed when FGF and Nodal signaling were inhibited. Our results suggest that, similar to other patterning systems, combinatorial signaling is likely to be a major driver of spatial diversity in BMP-dependent gene expression in zebrafish.
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Affiliation(s)
- Katherine W Rogers
- Systems Biology of Development Group, Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, Germany
| | - Mohammad ElGamacy
- Systems Biology of Development Group, Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, Germany.,Modeling Tumorigenesis Group, Translational Oncology Division, Eberhard Karls University Tübingen, Tübingen, Germany.,Heliopolis Biotechnology Ltd, London, United Kingdom
| | - Benjamin M Jordan
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, United States
| | - Patrick Müller
- Systems Biology of Development Group, Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, Germany.,Modeling Tumorigenesis Group, Translational Oncology Division, Eberhard Karls University Tübingen, Tübingen, Germany
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18
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Eck E, Liu J, Kazemzadeh-Atoufi M, Ghoreishi S, Blythe SA, Garcia HG. Quantitative dissection of transcription in development yields evidence for transcription-factor-driven chromatin accessibility. eLife 2020; 9:e56429. [PMID: 33074101 PMCID: PMC7738189 DOI: 10.7554/elife.56429] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Accepted: 10/16/2020] [Indexed: 12/28/2022] Open
Abstract
Thermodynamic models of gene regulation can predict transcriptional regulation in bacteria, but in eukaryotes, chromatin accessibility and energy expenditure may call for a different framework. Here, we systematically tested the predictive power of models of DNA accessibility based on the Monod-Wyman-Changeux (MWC) model of allostery, which posits that chromatin fluctuates between accessible and inaccessible states. We dissected the regulatory dynamics of hunchback by the activator Bicoid and the pioneer-like transcription factor Zelda in living Drosophila embryos and showed that no thermodynamic or non-equilibrium MWC model can recapitulate hunchback transcription. Therefore, we explored a model where DNA accessibility is not the result of thermal fluctuations but is catalyzed by Bicoid and Zelda, possibly through histone acetylation, and found that this model can predict hunchback dynamics. Thus, our theory-experiment dialogue uncovered potential molecular mechanisms of transcriptional regulatory dynamics, a key step toward reaching a predictive understanding of developmental decision-making.
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Affiliation(s)
- Elizabeth Eck
- Biophysics Graduate Group, University of California at BerkeleyBerkeleyUnited States
| | - Jonathan Liu
- Department of Physics, University of California at BerkeleyBerkeleyUnited States
| | | | - Sydney Ghoreishi
- Department of Molecular and Cell Biology, University of California at BerkeleyBerkeleyUnited States
| | - Shelby A Blythe
- Department of Molecular Biosciences, Northwestern UniversityEvanstonUnited States
| | - Hernan G Garcia
- Biophysics Graduate Group, University of California at BerkeleyBerkeleyUnited States
- Department of Physics, University of California at BerkeleyBerkeleyUnited States
- Department of Molecular and Cell Biology, University of California at BerkeleyBerkeleyUnited States
- Institute for Quantitative Biosciences-QB3, University of California at BerkeleyBerkeleyUnited States
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19
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Abstract
Key discoveries in Drosophila have shaped our understanding of cellular "enhancers." With a special focus on the fly, this chapter surveys properties of these adaptable cis-regulatory elements, whose actions are critical for the complex spatial/temporal transcriptional regulation of gene expression in metazoa. The powerful combination of genetics, molecular biology, and genomics available in Drosophila has provided an arena in which the developmental role of enhancers can be explored. Enhancers are characterized by diverse low- or high-throughput assays, which are challenging to interpret, as not all of these methods of identifying enhancers produce concordant results. As a model metazoan, the fly offers important advantages to comprehensive analysis of the central functions that enhancers play in gene expression, and their critical role in mediating the production of phenotypes from genotype and environmental inputs. A major challenge moving forward will be obtaining a quantitative understanding of how these cis-regulatory elements operate in development and disease.
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Affiliation(s)
- Stephen Small
- Department of Biology, Developmental Systems Training Program, New York University, 10003 and
| | - David N Arnosti
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
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20
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Koromila T, Stathopoulos A. Distinct Roles of Broadly Expressed Repressors Support Dynamic Enhancer Action and Change in Time. Cell Rep 2020; 28:855-863.e5. [PMID: 31340149 PMCID: PMC6927530 DOI: 10.1016/j.celrep.2019.06.063] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Revised: 05/02/2019] [Accepted: 06/17/2019] [Indexed: 10/26/2022] Open
Abstract
How broadly expressed repressors regulate gene expression is incompletely understood. To gain insight, we investigated how Suppressor of Hairless-Su(H)-and Runt regulate expression of bone morphogenetic protein (BMP) antagonist short-gastrulation via the sog_Distal enhancer. A live imaging protocol was optimized to capture this enhancer's spatiotemporal output throughout the early Drosophila embryo, finding in this context that Runt regulates transcription initiation, Su(H) regulates transcription rate, and both factors control spatial expression. Furthermore, whereas Su(H) functions as a dedicated repressor, Runt temporally switches from repressor to activator. Our results demonstrate that broad repressors play temporally distinct roles and contribute to dynamic gene expression. Both Run and Su(H)'s ability to influence the spatiotemporal domains of gene expression may serve to counterbalance activators and function in this manner as important regulators of the maternal-to-zygotic transition in early embryos.
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Affiliation(s)
- Theodora Koromila
- Division of Biology and Biological Engineering, California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125, USA
| | - Angelike Stathopoulos
- Division of Biology and Biological Engineering, California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125, USA.
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21
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Koromila T, Gao F, Iwasaki Y, He P, Pachter L, Gergen JP, Stathopoulos A. Odd-paired is a pioneer-like factor that coordinates with Zelda to control gene expression in embryos. eLife 2020; 9:e59610. [PMID: 32701060 PMCID: PMC7417190 DOI: 10.7554/elife.59610] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 07/22/2020] [Indexed: 01/29/2023] Open
Abstract
Pioneer factors such as Zelda (Zld) help initiate zygotic transcription in Drosophila early embryos, but whether other factors support this dynamic process is unclear. Odd-paired (Opa), a zinc-finger transcription factor expressed at cellularization, controls the transition of genes from pair-rule to segmental patterns along the anterior-posterior axis. Finding that Opa also regulates expression through enhancer sog_Distal along the dorso-ventral axis, we hypothesized Opa's role is more general. Chromatin-immunoprecipitation (ChIP-seq) confirmed its in vivo binding to sog_Distal but also identified widespread binding throughout the genome, comparable to Zld. Furthermore, chromatin assays (ATAC-seq) demonstrate that Opa, like Zld, influences chromatin accessibility genome-wide at cellularization, suggesting both are pioneer factors with common as well as distinct targets. Lastly, embryos lacking opa exhibit widespread, late patterning defects spanning both axes. Collectively, these data suggest Opa is a general timing factor and likely late-acting pioneer factor that drives a secondary wave of zygotic gene expression.
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Affiliation(s)
- Theodora Koromila
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - Fan Gao
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - Yasuno Iwasaki
- Stony Brook University, Department of Biochemistry and Cell Biology and Center for Developmental GeneticsStony BrookUnited States
| | - Peng He
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - Lior Pachter
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - J Peter Gergen
- Stony Brook University, Department of Biochemistry and Cell Biology and Center for Developmental GeneticsStony BrookUnited States
| | - Angelike Stathopoulos
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
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22
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Barbier I, Perez‐Carrasco R, Schaerli Y. Controlling spatiotemporal pattern formation in a concentration gradient with a synthetic toggle switch. Mol Syst Biol 2020; 16:e9361. [PMID: 32529808 PMCID: PMC7290156 DOI: 10.15252/msb.20199361] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Revised: 04/29/2020] [Accepted: 05/08/2020] [Indexed: 11/20/2022] Open
Abstract
The formation of spatiotemporal patterns of gene expression is frequently guided by gradients of diffusible signaling molecules. The toggle switch subnetwork, composed of two cross-repressing transcription factors, is a common component of gene regulatory networks in charge of patterning, converting the continuous information provided by the gradient into discrete abutting stripes of gene expression. We present a synthetic biology framework to understand and characterize the spatiotemporal patterning properties of the toggle switch. To this end, we built a synthetic toggle switch controllable by diffusible molecules in Escherichia coli. We analyzed the patterning capabilities of the circuit by combining quantitative measurements with a mathematical reconstruction of the underlying dynamical system. The toggle switch can produce robust patterns with sharp boundaries, governed by bistability and hysteresis. We further demonstrate how the hysteresis, position, timing, and precision of the boundary can be controlled, highlighting the dynamical flexibility of the circuit.
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Affiliation(s)
- Içvara Barbier
- Department of Fundamental MicrobiologyUniversity of LausanneLausanneSwitzerland
| | - Rubén Perez‐Carrasco
- Department of Life SciencesImperial College LondonSouth Kensington CampusLondonUK
- Department of MathematicsUniversity College LondonLondonUK
| | - Yolanda Schaerli
- Department of Fundamental MicrobiologyUniversity of LausanneLausanneSwitzerland
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23
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Peter IS. The function of architecture and logic in developmental gene regulatory networks. Curr Top Dev Biol 2020; 139:267-295. [PMID: 32450963 DOI: 10.1016/bs.ctdb.2020.04.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
An important contribution of systems biology is the insight that biological systems depend on the function of molecular interactions and not just on individual molecules. System level mechanisms are particularly important in the development of animals and plants which depends not just on transcription factors and signaling molecules, but also on regulatory circuits and gene regulatory networks (GRNs). However, since GRNs consist of transcription factors, it can be challenging to assess the function of regulatory circuits independently of the function of regulatory factors. The comparison of different GRNs offers a way to do so and leads to several observations. First, similar regulatory circuits operate in various developmental contexts and in different species, and frequently, these circuits are associated with similar developmental functions. Second, given regulatory circuits are often used at particular positions within the GRN hierarchy. Third, in some GRNs, regulatory circuits are organized in a particular order in respect to each other. And fourth, the evolution of GRNs occurs not just by co-option of regulatory genes but also by rewiring of regulatory linkages between conserved regulatory genes, indicating that the organization of interactions is important. Thus, even though in most instances the function of regulatory circuits remains to be discovered, it becomes evident that the architecture and logic of GRNs are functionally important for the control of genome activity and for the specification of the body plan.
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Affiliation(s)
- Isabelle S Peter
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States.
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24
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Camacho-Aguilar E, Warmflash A. Insights into mammalian morphogen dynamics from embryonic stem cell systems. Curr Top Dev Biol 2020; 137:279-305. [PMID: 32143746 PMCID: PMC7713707 DOI: 10.1016/bs.ctdb.2019.11.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Morphogens play an essential role in cell fate specification and patterning including in laying out the mammalian body plan during gastrulation. In vivo studies have shed light on the signaling pathways involved in this process and the phenotypes associated with their disruption, however, several important open questions remain regarding how morphogens function in space and time. Self-organized patterning systems based on embryonic stem cells have emerged as a powerful platform for beginning to address these questions that is complementary to in vivo approaches. Here we review recent progress in understanding morphogen signaling dynamics and patterning in early mammalian development by taking advantage of cutting-edge embryonic stem cell technology.
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Affiliation(s)
| | - Aryeh Warmflash
- Department of Biosciences, Rice University, Houston, TX, United States; Department of Bioengineering, Rice University, Houston, TX, United States.
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25
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Chen H, Gregor T. Using RNA Tags for Multicolor Live Imaging of Chromatin Loci and Transcription in Drosophila Embryos. Methods Mol Biol 2020; 2166:373-384. [PMID: 32710421 PMCID: PMC8130451 DOI: 10.1007/978-1-0716-0712-1_22] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Elucidating the biological implications of higher order chromatin architectures in animal development requires simultaneous, quantitative measurements of chromatin dynamics and transcriptional activity in living specimen. Here we describe a multicolor labeling and live imaging approach in embryos of the fruit fly Drosophila melanogaster. The method allows simultaneous measurement of movements of specific loci and their transcriptional activity for developmental genes, enabling new approaches to probe the interaction between 3D chromatin architecture and regulation of gene expression in development.
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Affiliation(s)
- Hongtao Chen
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA
| | - Thomas Gregor
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA.
- Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ, USA.
- Department of Developmental and Stem Cell Biology, UMR3738, Institut Pasteur, Paris, France.
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26
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Abstract
Spatially distributed signaling molecules, known as morphogens, provide spatial information during development. A host of different morphogens have now been identified, from subcellular gradients through to morphogens that act across a whole embryo. These gradients form over a wide-range of timescales, from seconds to hours, and their time windows for interpretation are also highly variable; the processes of morphogen gradient formation and interpretation are highly dynamic. The morphogen Bicoid (Bcd), present in the early Drosophila embryo, is essential for setting up the future Drosophila body segments. Due to its accessibility for both genetic perturbations and imaging, this system has provided key insights into how precise patterning can occur within a highly dynamic system. Here, we review the temporal scales of Bcd gradient formation and interpretation. In particular, we discuss the quantitative evidence for different models of Bcd gradient formation, outline the time windows for Bcd interpretation, and describe how Bcd temporally adapts its own ability to be interpreted. The utilization of temporal information in morphogen readout may provide crucial inputs to ensure precise spatial patterning, particularly in rapidly developing systems.
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27
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Schloop AE, Bandodkar PU, Reeves GT. Formation, interpretation, and regulation of the Drosophila Dorsal/NF-κB gradient. Curr Top Dev Biol 2019; 137:143-191. [PMID: 32143742 DOI: 10.1016/bs.ctdb.2019.11.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The morphogen gradient of the transcription factor Dorsal in the early Drosophila embryo has become one of the most widely studied tissue patterning systems. Dorsal is a Drosophila homolog of mammalian NF-κB and patterns the dorsal-ventral axis of the blastoderm embryo into several tissue types by spatially regulating upwards of 100 zygotic genes. Recent studies using fluorescence microscopy and live imaging have quantified the Dorsal gradient and its target genes, which has paved the way for mechanistic modeling of the gradient. In this review, we describe the mechanisms behind the initiation of the Dorsal gradient and its regulation of target genes. The main focus of the review is a discussion of quantitative and computational studies of the Dl gradient system, including regulation of the Dl gradient. We conclude with a discussion of potential future directions.
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Affiliation(s)
- Allison E Schloop
- Genetics Program, North Carolina State University, Raleigh, NC, United States
| | - Prasad U Bandodkar
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, United States
| | - Gregory T Reeves
- Genetics Program, North Carolina State University, Raleigh, NC, United States; Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, United States.
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28
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Rogers KW, Müller P. Optogenetic approaches to investigate spatiotemporal signaling during development. Curr Top Dev Biol 2019; 137:37-77. [PMID: 32143750 DOI: 10.1016/bs.ctdb.2019.11.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Embryogenesis is coordinated by signaling pathways that pattern the developing organism. Many aspects of this process are not fully understood, including how signaling molecules spread through embryonic tissues, how signaling amplitude and dynamics are decoded, and how multiple signaling pathways cooperate to pattern the body plan. Optogenetic approaches can be used to address these questions by providing precise experimental control over a variety of biological processes. Here, we review how these strategies have provided new insights into developmental signaling and discuss how they could contribute to future investigations.
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Affiliation(s)
- Katherine W Rogers
- Systems Biology of Development Group, Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, Germany
| | - Patrick Müller
- Systems Biology of Development Group, Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, Germany; Modeling Tumorigenesis Group, Translational Oncology Division, Eberhard Karls University Tübingen, Tübingen, Germany.
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29
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Abstract
Drosophila melanogaster embryos develop initially as a syncytium of totipotent nuclei and subsequently, once cellularized, undergo morphogenetic movements associated with gastrulation to generate the three somatic germ layers of the embryo: mesoderm, ectoderm, and endoderm. In this chapter, we focus on the first phase of gastrulation in Drosophila involving patterning of early embryos when cells differentiate their gene expression programs. This patterning process requires coordination of multiple developmental processes including genome reprogramming at the maternal-to-zygotic transition, combinatorial action of transcription factors to support distinct gene expression, and dynamic feedback between this genetic patterning by transcription factors and changes in cell morphology. We discuss the gene regulatory programs acting during patterning to specify the three germ layers, which involve the regulation of spatiotemporal gene expression coupled to physical tissue morphogenesis.
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Affiliation(s)
- Angelike Stathopoulos
- Division of Biology & Biological Engineering, California Institute of Technology, Pasadena, CA, United States.
| | - Susan Newcomb
- Division of Biology & Biological Engineering, California Institute of Technology, Pasadena, CA, United States
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30
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Garcia HG, Berrocal A, Kim YJ, Martini G, Zhao J. Lighting up the central dogma for predictive developmental biology. Curr Top Dev Biol 2019; 137:1-35. [PMID: 32143740 DOI: 10.1016/bs.ctdb.2019.10.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Although the last 30years have witnessed the mapping of the wiring diagrams of the gene regulatory networks that dictate cell fate and animal body plans, specific understanding building on such network diagrams that shows how DNA regulatory regions control gene expression lags far behind. These networks have yet to yield the predictive power necessary to, for example, calculate how the concentration dynamics of input transcription factors and DNA regulatory sequence prescribes output patterns of gene expression that, in turn, determine body plans themselves. Here, we argue that reaching a predictive understanding of developmental decision-making calls for an interplay between theory and experiment aimed at revealing how the regulation of the processes of the central dogma dictate network connections and how network topology guides cells toward their ultimate developmental fate. To make this possible, it is crucial to break free from the snapshot-based understanding of embryonic development facilitated by fixed-tissue approaches and embrace new technologies that capture the dynamics of developmental decision-making at the single cell level, in living embryos.
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Affiliation(s)
- Hernan G Garcia
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA, United States; Department of Physics, University of California at Berkeley, Berkeley, CA, United States; Biophysics Graduate Group, University of California at Berkeley, Berkeley, CA, United States; Quantitative Biosciences-QB3, University of California at Berkeley, Berkeley, CA, United States.
| | - Augusto Berrocal
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA, United States
| | - Yang Joon Kim
- Biophysics Graduate Group, University of California at Berkeley, Berkeley, CA, United States
| | - Gabriella Martini
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA, United States
| | - Jiaxi Zhao
- Department of Physics, University of California at Berkeley, Berkeley, CA, United States
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31
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Bicoid-Dependent Activation of the Target Gene hunchback Requires a Two-Motif Sequence Code in a Specific Basal Promoter. Mol Cell 2019; 75:1178-1187.e4. [PMID: 31402096 DOI: 10.1016/j.molcel.2019.06.038] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 05/14/2019] [Accepted: 06/25/2019] [Indexed: 01/08/2023]
Abstract
In complex genetic loci, individual enhancers interact most often with specific basal promoters. Here we investigate the activation of the Bicoid target gene hunchback (hb), which contains two basal promoters (P1 and P2). Early in embryogenesis, P1 is silent, while P2 is strongly activated. In vivo deletion of P2 does not cause activation of P1, suggesting that P2 contains intrinsic sequence motifs required for activation. We show that a two-motif code (a Zelda binding site plus TATA) is required and sufficient for P2 activation. Zelda sites are present in the promoters of many embryonically expressed genes, but the combination of Zelda plus TATA does not seem to be a general code for early activation or Bicoid-specific activation per se. Because Zelda sites are also found in Bicoid-dependent enhancers, we propose that simultaneous binding to both enhancers and promoters independently synchronizes chromatin accessibility and facilitates correct enhancer-promoter interactions.
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32
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Vuilleumier R, Lian T, Flibotte S, Khan ZN, Fuchs A, Pyrowolakis G, Allan DW. Retrograde BMP signaling activates neuronal gene expression through widespread deployment of a conserved BMP-responsive cis-regulatory activation element. Nucleic Acids Res 2019; 47:679-699. [PMID: 30476189 PMCID: PMC6344883 DOI: 10.1093/nar/gky1135] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Accepted: 10/25/2018] [Indexed: 12/29/2022] Open
Abstract
Retrograde Bone Morphogenetic Protein (BMP) signaling in neurons is essential for the differentiation and synaptic function of many neuronal subtypes. BMP signaling regulates these processes via Smad transcription factor activity, yet the scope and nature of Smad-dependent gene regulation in neurons are mostly unknown. Here, we applied a computational approach to predict Smad-binding cis-regulatory BMP-Activating Elements (BMP-AEs) in Drosophila, followed by transgenic in vivo reporter analysis to test their neuronal subtype enhancer activity in the larval central nervous system (CNS). We identified 34 BMP-AE-containing genomic fragments that are responsive to BMP signaling in neurons, and showed that the embedded BMP-AEs are required for this activity. RNA-seq analysis identified BMP-responsive genes in the CNS and revealed that BMP-AEs selectively enrich near BMP-activated genes. These data suggest that functional BMP-AEs control nearby BMP-activated genes, which we validated experimentally. Finally, we demonstrated that the BMP-AE motif mediates a conserved Smad-responsive function in the Drosophila and vertebrate CNS. Our results provide evidence that BMP signaling controls neuronal function by directly coordinating the expression of a battery of genes through widespread deployment of a conserved Smad-responsive cis-regulatory motif.
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Affiliation(s)
- Robin Vuilleumier
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Tianshun Lian
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Stephane Flibotte
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Zaynah N Khan
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Alisa Fuchs
- BIOSS, Centre for Biological Signaling Studies and Institute for Biology I, Faculty of Biology, Albert-Ludwigs University of Freiburg, Freiburg, Germany.,Max-Planck Institute for Molecular Genetics, Berlin, Germany
| | - George Pyrowolakis
- BIOSS, Centre for Biological Signaling Studies and Institute for Biology I, Faculty of Biology, Albert-Ludwigs University of Freiburg, Freiburg, Germany
| | - Douglas W Allan
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
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Park J, Estrada J, Johnson G, Vincent BJ, Ricci-Tam C, Bragdon MDJ, Shulgina Y, Cha A, Wunderlich Z, Gunawardena J, DePace AH. Dissecting the sharp response of a canonical developmental enhancer reveals multiple sources of cooperativity. eLife 2019; 8:e41266. [PMID: 31223115 PMCID: PMC6588347 DOI: 10.7554/elife.41266] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 03/04/2019] [Indexed: 12/19/2022] Open
Abstract
Developmental enhancers integrate graded concentrations of transcription factors (TFs) to create sharp gene expression boundaries. Here we examine the hunchback P2 (HbP2) enhancer which drives a sharp expression pattern in the Drosophila blastoderm embryo in response to the transcriptional activator Bicoid (Bcd). We systematically interrogate cis and trans factors that influence the shape and position of expression driven by HbP2, and find that the prevailing model, based on pairwise cooperative binding of Bcd to HbP2 is not adequate. We demonstrate that other proteins, such as pioneer factors, Mediator and histone modifiers influence the shape and position of the HbP2 expression pattern. Comparing our results to theory reveals how higher-order cooperativity and energy expenditure impact boundary location and sharpness. Our results emphasize that the bacterial view of transcription regulation, where pairwise interactions between regulatory proteins dominate, must be reexamined in animals, where multiple molecular mechanisms collaborate to shape the gene regulatory function.
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Affiliation(s)
- Jeehae Park
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | - Javier Estrada
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | - Gemma Johnson
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | - Ben J Vincent
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | - Chiara Ricci-Tam
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | - Meghan DJ Bragdon
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | | | - Anna Cha
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | - Zeba Wunderlich
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
| | | | - Angela H DePace
- Department of Systems BiologyHarvard Medical SchoolBostonUnited States
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34
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Galstyan V, Funk L, Einav T, Phillips R. Combinatorial Control through Allostery. J Phys Chem B 2019; 123:2792-2800. [PMID: 30768906 DOI: 10.1021/acs.jpcb.8b12517] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Many instances of cellular signaling and transcriptional regulation involve switch-like molecular responses to the presence or absence of input ligands. To understand how these responses come about and how they can be harnessed, we develop a statistical mechanical model to characterize the types of Boolean logic that can arise from allosteric molecules following the Monod-Wyman-Changeux (MWC) model. Building upon previous work, we show how an allosteric molecule regulated by two inputs can elicit AND, OR, NAND, and NOR responses but is unable to realize XOR or XNOR gates. Next, we demonstrate the ability of an MWC molecule to perform ratiometric sensing-a response behavior where activity depends monotonically on the ratio of ligand concentrations. We then extend our analysis to more general schemes of combinatorial control involving either additional binding sites for the two ligands or an additional third ligand and show how these additions can cause a switch in the logic behavior of the molecule. Overall, our results demonstrate the wide variety of control schemes that biological systems can implement using simple mechanisms.
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Affiliation(s)
| | - Luke Funk
- Harvard-MIT Division of Health Sciences and Technology and the Broad Institute of MIT and Harvard , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
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35
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A cell cycle-coordinated Polymerase II transcription compartment encompasses gene expression before global genome activation. Nat Commun 2019; 10:691. [PMID: 30741925 PMCID: PMC6370886 DOI: 10.1038/s41467-019-08487-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Accepted: 01/02/2019] [Indexed: 02/07/2023] Open
Abstract
Most metazoan embryos commence development with rapid, transcriptionally silent cell divisions, with genome activation delayed until the mid-blastula transition (MBT). However, a set of genes escapes global repression and gets activated before MBT. Here we describe the formation and the spatio-temporal dynamics of a pair of distinct transcription compartments, which encompasses the earliest gene expression in zebrafish. 4D imaging of pri-miR430 and zinc-finger-gene activities by a novel, native transcription imaging approach reveals transcriptional sharing of nuclear compartments, which are regulated by homologous chromosome organisation. These compartments carry the majority of nascent-RNAs and active Polymerase II, are chromatin-depleted and represent the main sites of detectable transcription before MBT. Transcription occurs during the S-phase of increasingly permissive cleavage cycles. It is proposed, that the transcription compartment is part of the regulatory architecture of embryonic nuclei and offers a transcriptionally competent environment to facilitate early escape from repression before global genome activation. Transcription is globally repressed in early stage of embryo development, but a set of genes including pri-miR-430 and zinc finger genes is known to escape the repression. Here the authors image the very first transcriptional activities in the living zebra fish embryo, demonstrating a cell cycle-coordinated polymerase II transcription compartment.
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36
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Surkova S, Golubkova E, Mamon L, Samsonova M. Dynamic maternal gradients and morphogenetic networks in Drosophila early embryo. Biosystems 2018; 173:207-213. [DOI: 10.1016/j.biosystems.2018.10.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Revised: 10/06/2018] [Accepted: 10/08/2018] [Indexed: 11/30/2022]
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37
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Liu Q, Onal P, Datta RR, Rogers JM, Schmidt-Ott U, Bulyk ML, Small S, Thornton JW. Ancient mechanisms for the evolution of the bicoid homeodomain's function in fly development. eLife 2018; 7:e34594. [PMID: 30298815 PMCID: PMC6177261 DOI: 10.7554/elife.34594] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 07/28/2018] [Indexed: 12/14/2022] Open
Abstract
The ancient mechanisms that caused developmental gene regulatory networks to diversify among distantly related taxa are not well understood. Here we use ancestral protein reconstruction, biochemical experiments, and developmental assays of transgenic animals carrying reconstructed ancestral genes to investigate how the transcription factor Bicoid (Bcd) evolved its central role in anterior-posterior patterning in flies. We show that most of Bcd's derived functions are attributable to evolutionary changes within its homeodomain (HD) during a phylogenetic interval >140 million years ago. A single substitution from this period (Q50K) accounts almost entirely for the evolution of Bcd's derived DNA specificity in vitro. In transgenic embryos expressing the reconstructed ancestral HD, however, Q50K confers activation of only a few of Bcd's transcriptional targets and yields a very partial rescue of anterior development. Adding a second historical substitution (M54R) confers regulation of additional Bcd targets and further rescues anterior development. These results indicate that two epistatically interacting mutations played a major role in the evolution of Bcd's controlling regulatory role in early development. They also show how ancestral sequence reconstruction can be combined with in vivo characterization of transgenic animals to illuminate the historical mechanisms of developmental evolution.
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Affiliation(s)
- Qinwen Liu
- Department of Ecology and EvolutionUniversity of ChicagoChicagoUnited States
| | - Pinar Onal
- Department of BiologyNew York UniversityNew YorkUnited States
| | - Rhea R Datta
- Department of BiologyNew York UniversityNew YorkUnited States
| | - Julia M Rogers
- Committee on Higher Degrees in BiophysicsHarvard UniversityCambridgeUnited States
- Division of Genetics, Department of MedicineBrigham and Women’s Hospital and Harvard Medical SchoolBostonUnited States
| | - Urs Schmidt-Ott
- Department of Organismal Biology and AnatomyUniversity of ChicagoChicagoUnited States
| | - Martha L Bulyk
- Committee on Higher Degrees in BiophysicsHarvard UniversityCambridgeUnited States
- Division of Genetics, Department of MedicineBrigham and Women’s Hospital and Harvard Medical SchoolBostonUnited States
- Department of PathologyBrigham and Women’s Hospital and Harvard Medical SchoolBostonUnited States
| | - Stephen Small
- Department of BiologyNew York UniversityNew YorkUnited States
| | - Joseph W Thornton
- Department of Ecology and EvolutionUniversity of ChicagoChicagoUnited States
- Department of Human GeneticsUniversity of ChicagoChicagoUnited States
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38
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Lucas T, Tran H, Perez Romero CA, Guillou A, Fradin C, Coppey M, Walczak AM, Dostatni N. 3 minutes to precisely measure morphogen concentration. PLoS Genet 2018; 14:e1007676. [PMID: 30365533 PMCID: PMC6221364 DOI: 10.1371/journal.pgen.1007676] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 11/07/2018] [Accepted: 09/05/2018] [Indexed: 11/18/2022] Open
Abstract
Morphogen gradients provide concentration-dependent positional information along polarity axes. Although the dynamics of the establishment of these gradients is well described, precision and noise in the downstream activation processes remain elusive. A simple paradigm to address these questions is the Bicoid morphogen gradient that elicits a rapid step-like transcriptional response in young fruit fly embryos. Focusing on the expression of the major Bicoid target, hunchback (hb), at the onset of zygotic transcription, we used the MS2-MCP approach which combines fluorescent labeling of nascent mRNA with live imaging at high spatial and temporal resolution. Removing 36 putative Zelda binding sites unexpectedly present in the original MS2 reporter, we show that the 750 bp of the hb promoter are sufficient to recapitulate endogenous expression at the onset of zygotic transcription. After each mitosis, in the anterior, expression is turned on to rapidly reach a plateau with all nuclei expressing the reporter. Consistent with a Bicoid dose-dependent activation process, the time period required to reach the plateau increases with the distance to the anterior pole. Despite the challenge imposed by frequent mitoses and high nuclei-to-nuclei variability in transcription kinetics, it only takes 3 minutes at each interphase for the MS2 reporter loci to distinguish subtle differences in Bicoid concentration and establish a steadily positioned and steep (Hill coefficient ~ 7) expression boundary. Modeling based on the cooperativity between the 6 known Bicoid binding sites in the hb promoter region, assuming rate limiting concentrations of the Bicoid transcription factor at the boundary, is able to capture the observed dynamics of pattern establishment but not the steepness of the boundary. This suggests that a simple model based only on the cooperative binding of Bicoid is not sufficient to describe the spatiotemporal dynamics of early hb expression.
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Affiliation(s)
- Tanguy Lucas
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
| | - Huy Tran
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
- Ecole Normale Supérieure, PSL Research University, CNRS, Sorbonne Université, Physique Théorique, Paris, France
| | - Carmina Angelica Perez Romero
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
- Dept. of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
| | - Aurélien Guillou
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
| | - Cécile Fradin
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
- Dept. of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
| | - Mathieu Coppey
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Physico Chimie, Paris, France
| | - Aleksandra M. Walczak
- Ecole Normale Supérieure, PSL Research University, CNRS, Sorbonne Université, Physique Théorique, Paris, France
| | - Nathalie Dostatni
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
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39
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Datta RR, Ling J, Kurland J, Ren X, Xu Z, Yucel G, Moore J, Shokri L, Baker I, Bishop T, Struffi P, Levina R, Bulyk ML, Johnston RJ, Small S. A feed-forward relay integrates the regulatory activities of Bicoid and Orthodenticle via sequential binding to suboptimal sites. Genes Dev 2018; 32:723-736. [PMID: 29764918 PMCID: PMC6004077 DOI: 10.1101/gad.311985.118] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 04/17/2018] [Indexed: 11/25/2022]
Abstract
Datta et al. define three major classes of enhancers that are differentially sensitive to binding and transcriptional activation by Bicoid (Bcd) and Orthodenticle (Otd). The specific activities of enhancers in each class are mediated by DNA motif variants preferentially bound by Bcd or Otd and the presence or absence of sites for cofactors that interact with these proteins. The K50 (lysine at amino acid position 50) homeodomain (HD) protein Orthodenticle (Otd) is critical for anterior patterning and brain and eye development in most metazoans. In Drosophila melanogaster, another K50HD protein, Bicoid (Bcd), has evolved to replace Otd's ancestral function in embryo patterning. Bcd is distributed as a long-range maternal gradient and activates transcription of a large number of target genes, including otd. Otd and Bcd bind similar DNA sequences in vitro, but how their transcriptional activities are integrated to pattern anterior regions of the embryo is unknown. Here we define three major classes of enhancers that are differentially sensitive to binding and transcriptional activation by Bcd and Otd. Class 1 enhancers are initially activated by Bcd, and activation is transferred to Otd via a feed-forward relay (FFR) that involves sequential binding of the two proteins to the same DNA motif. Class 2 enhancers are activated by Bcd and maintained by an Otd-independent mechanism. Class 3 enhancers are never bound by Bcd, but Otd binds and activates them in a second wave of zygotic transcription. The specific activities of enhancers in each class are mediated by DNA motif variants preferentially bound by Bcd or Otd and the presence or absence of sites for cofactors that interact with these proteins. Our results define specific patterning roles for Bcd and Otd and provide mechanisms for coordinating the precise timing of gene expression patterns during embryonic development.
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Affiliation(s)
- Rhea R Datta
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Jia Ling
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Jesse Kurland
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.,Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Xiaotong Ren
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Zhe Xu
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Gozde Yucel
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Jackie Moore
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Leila Shokri
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.,Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Isabel Baker
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Timothy Bishop
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Paolo Struffi
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Rimma Levina
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Martha L Bulyk
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.,Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Robert J Johnston
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Stephen Small
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
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40
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Clark E, Peel AD. Evidence for the temporal regulation of insect segmentation by a conserved sequence of transcription factors. Development 2018; 145:dev.155580. [PMID: 29724758 PMCID: PMC6001374 DOI: 10.1242/dev.155580] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 04/25/2018] [Indexed: 01/20/2023]
Abstract
Long-germ insects, such as the fruit fly Drosophila melanogaster, pattern their segments simultaneously, whereas short-germ insects, such as the beetle Tribolium castaneum, pattern their segments sequentially, from anterior to posterior. While the two modes of segmentation at first appear quite distinct, much of this difference might simply reflect developmental heterochrony. We now show here that, in both Drosophila and Tribolium, segment patterning occurs within a common framework of sequential Caudal, Dichaete, and Odd-paired expression. In Drosophila these transcription factors are expressed like simple timers within the blastoderm, while in Tribolium they form wavefronts that sweep from anterior to posterior across the germband. In Drosophila, all three are known to regulate pair-rule gene expression and influence the temporal progression of segmentation. We propose that these regulatory roles are conserved in short-germ embryos, and that therefore the changing expression profiles of these genes across insects provide a mechanistic explanation for observed differences in the timing of segmentation. In support of this hypothesis we demonstrate that Odd-paired is essential for segmentation in Tribolium, contrary to previous reports.
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Affiliation(s)
- Erik Clark
- Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, UK
| | - Andrew D Peel
- Faculty of Biological Sciences, University of Leeds, UK
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41
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Haines JE, Eisen MB. Patterns of chromatin accessibility along the anterior-posterior axis in the early Drosophila embryo. PLoS Genet 2018; 14:e1007367. [PMID: 29727464 PMCID: PMC5955596 DOI: 10.1371/journal.pgen.1007367] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 05/16/2018] [Accepted: 04/17/2018] [Indexed: 12/20/2022] Open
Abstract
As the Drosophila embryo transitions from the use of maternal RNAs to zygotic transcription, domains of open chromatin, with relatively low nucleosome density and specific histone marks, are established at promoters and enhancers involved in patterned embryonic transcription. However it remains unclear how regions of activity are established during early embryogenesis, and if they are the product of spatially restricted or ubiquitous processes. To shed light on this question, we probed chromatin accessibility across the anterior-posterior axis (A-P) of early Drosophila melanogaster embryos by applying a transposon based assay for chromatin accessibility (ATAC-seq) to anterior and posterior halves of hand-dissected, cellular blastoderm embryos. We find that genome-wide chromatin accessibility is highly similar between the two halves, with regions that manifest significant accessibility in one half of the embryo almost always accessible in the other half, even for promoters that are active in exclusively one half of the embryo. These data support previous studies that show that chromatin accessibility is not a direct result of activity, and point to a role for ubiquitous factors or processes in establishing chromatin accessibility at promoters in the early embryo. However, in concordance with similar works, we find that at enhancers active exclusively in one half of the embryo, we observe a significant skew towards greater accessibility in the region of their activity, highlighting the role of patterning factors such as Bicoid in this process.
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Affiliation(s)
- Jenna E. Haines
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States of America
| | - Michael B. Eisen
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States of America
- Department of Integrative Biology, University of California, Berkeley, Berkeley, United States of America
- Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States of America
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42
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Capicua controls Toll/IL-1 signaling targets independently of RTK regulation. Proc Natl Acad Sci U S A 2018; 115:1807-1812. [PMID: 29432195 DOI: 10.1073/pnas.1713930115] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The HMG-box protein Capicua (Cic) is a conserved transcriptional repressor that functions downstream of receptor tyrosine kinase (RTK) signaling pathways in a relatively simple switch: In the absence of signaling, Cic represses RTK-responsive genes by binding to nearly invariant sites in DNA, whereas activation of RTK signaling down-regulates Cic activity, leading to derepression of its targets. This mechanism controls gene expression in both Drosophila and mammals, but whether Cic can also function via other regulatory mechanisms remains unknown. Here, we characterize an RTK-independent role of Cic in regulating spatially restricted expression of Toll/IL-1 signaling targets in Drosophila embryogenesis. We show that Cic represses those targets by binding to suboptimal DNA sites of lower affinity than its known consensus sites. This binding depends on Dorsal/NF-κB, which translocates into the nucleus upon Toll activation and binds next to the Cic sites. As a result, Cic binds to and represses Toll targets only in regions with nuclear Dorsal. These results reveal a mode of Cic regulation unrelated to the well-established RTK/Cic depression axis and implicate cooperative binding in conjunction with low-affinity binding sites as an important mechanism of enhancer regulation. Given that Cic plays a role in many developmental and pathological processes in mammals, our results raise the possibility that some of these Cic functions are independent of RTK regulation and may depend on cofactor-assisted DNA binding.
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43
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Abstract
mRNA synthesis is one of the earliest readouts of the activity of a transcribed gene, which is of particular interest in the context of metazoan cell fate specification. These processes are intrinsically dynamic and stochastic, which makes in vivo single-cell measurements inevitable. Here, we present the application of a technology that has been widely used in single celled organisms to measure transcriptional activity in developing embryos of the fruit fly Drosophila melanogaster. The method allows for quantification of instantaneous polymerase occupancy of active gene loci and thereby enables the development and testing of models of gene regulation in development.
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44
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Rogers KW, Lord ND, Gagnon JA, Pauli A, Zimmerman S, Aksel DC, Reyon D, Tsai SQ, Joung JK, Schier AF. Nodal patterning without Lefty inhibitory feedback is functional but fragile. eLife 2017; 6. [PMID: 29215332 PMCID: PMC5720593 DOI: 10.7554/elife.28785] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 11/07/2017] [Indexed: 12/12/2022] Open
Abstract
Developmental signaling pathways often activate their own inhibitors. Such inhibitory feedback has been suggested to restrict the spatial and temporal extent of signaling or mitigate signaling fluctuations, but these models are difficult to rigorously test. Here, we determine whether the ability of the mesendoderm inducer Nodal to activate its inhibitor Lefty is required for development. We find that zebrafish lefty mutants exhibit excess Nodal signaling and increased specification of mesendoderm, resulting in embryonic lethality. Strikingly, development can be fully restored without feedback: Lethal patterning defects in lefty mutants can be rescued by ectopic expression of lefty far from its normal expression domain or by spatially and temporally uniform exposure to a Nodal inhibitor drug. While drug-treated mutants are less tolerant of mild perturbations to Nodal signaling levels than wild type embryos, they can develop into healthy adults. These results indicate that patterning without inhibitory feedback is functional but fragile. During animal development, a single fertilized cell gives rise to different tissues and organs. This ‘patterning’ process depends on signaling molecules that instruct cells in different positions in the embryo to acquire different identities. To avoid mistakes during patterning, each cell must receive the correct amount of signal at the appropriate time. In a process called ‘inhibitory feedback’, a signaling molecule instructs cells to produce molecules that block its own signaling. Although inhibitory feedback is widely used during patterning in organisms ranging from sea urchins to mammals, its exact purpose is often not clear. In part this is because feedback is challenging to experimentally manipulate. Removing the inhibitor disrupts feedback, but also increases signaling. Since the effects of broken feedback and increased signaling are intertwined, any resulting developmental defects do not provide information about what feedback specifically does. In order to examine the role of feedback, it is therefore necessary to disconnect the production of the inhibitor from the signaling process. In developing embryos, a well-known signaling molecule called Nodal instructs cells to become specific types – for example, a heart or gut cell. Nodal also promotes the production of its inhibitor, Lefty. To understand how this feedback system works, Rogers, Lord et al. first removed Lefty from zebrafish embryos. These embryos had excessive levels of Nodal signaling, did not develop correctly, and could not survive. Bathing the embryos in a drug that inhibits Nodal reduced excess signaling and allowed them to develop successfully. In these drug-treated embryos, inhibitor production is disconnected from the signaling process, allowing the role of feedback to be examined. Drug-treated embryos were less able to tolerate fluctuations in Nodal signaling than normal zebrafish embryos, which could compensate for such disturbances by adjusting Lefty levels. Overall, it appears that inhibitory feedback in this patterning system is important to compensate for alterations in Nodal signaling, but is not essential for development. Understanding the role of inhibitory feedback will be useful for efforts to grow tissues and organs in the laboratory for clinical use. The results presented by Rogers, Lord et al. also suggest the possibility that drug treatments could be developed to help correct birth defects in the womb.
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Affiliation(s)
- Katherine W Rogers
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - Nathan D Lord
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - James A Gagnon
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - Andrea Pauli
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - Steven Zimmerman
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - Deniz C Aksel
- Program in Biophysics, Harvard Medical School, Boston, United States
| | - Deepak Reyon
- Molecular Pathology Unit, Massachusetts General Hospital, Charlestown, United States.,Department of Pathology, Harvard Medical School, Boston, United States.,Center for Computational and Integrative Biology, Massachusetts General Hospital, Boston, United States.,Center for Cancer Research, Massachusetts General Hospital, Charlestown, United States
| | - Shengdar Q Tsai
- Molecular Pathology Unit, Massachusetts General Hospital, Charlestown, United States.,Department of Pathology, Harvard Medical School, Boston, United States.,Center for Computational and Integrative Biology, Massachusetts General Hospital, Boston, United States.,Center for Cancer Research, Massachusetts General Hospital, Charlestown, United States
| | - J Keith Joung
- Molecular Pathology Unit, Massachusetts General Hospital, Charlestown, United States.,Department of Pathology, Harvard Medical School, Boston, United States.,Center for Computational and Integrative Biology, Massachusetts General Hospital, Boston, United States.,Center for Cancer Research, Massachusetts General Hospital, Charlestown, United States
| | - Alexander F Schier
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.,Broad Institute of MIT and Harvard University, Cambridge, United States.,Center for Brain Science, Harvard University, Cambridge, United States.,Harvard Stem Cell Institute, Harvard University, Cambridge, United States.,Center for Systems Biology, Harvard University, Cambridge, United States
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45
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Tewary M, Ostblom J, Prochazka L, Zulueta-Coarasa T, Shakiba N, Fernandez-Gonzalez R, Zandstra PW. A stepwise model of reaction-diffusion and positional information governs self-organized human peri-gastrulation-like patterning. Development 2017; 144:4298-4312. [PMID: 28870989 PMCID: PMC5769627 DOI: 10.1242/dev.149658] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Accepted: 08/23/2017] [Indexed: 12/15/2022]
Abstract
How position-dependent cell fate acquisition occurs during embryogenesis is a central question in developmental biology. To study this process, we developed a defined, high-throughput assay to induce peri-gastrulation-associated patterning in geometrically confined human pluripotent stem cell (hPSC) colonies. We observed that, upon BMP4 treatment, phosphorylated SMAD1 (pSMAD1) activity in the colonies organized into a radial gradient. We developed a reaction-diffusion (RD)-based computational model and observed that the self-organization of pSMAD1 signaling was consistent with the RD principle. Consequent fate acquisition occurred as a function of both pSMAD1 signaling strength and duration of induction, consistent with the positional-information (PI) paradigm. We propose that the self-organized peri-gastrulation-like fate patterning in BMP4-treated geometrically confined hPSC colonies arises via a stepwise model of RD followed by PI. This two-step model predicted experimental responses to perturbations of key parameters such as colony size and BMP4 dose. Furthermore, it also predicted experimental conditions that resulted in RD-like periodic patterning in large hPSC colonies, and rescued peri-gastrulation-like patterning in colony sizes previously thought to be reticent to this behavior.
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Affiliation(s)
- Mukul Tewary
- Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Collaborative Program in Developmental Biology, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
| | - Joel Ostblom
- Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
| | - Laura Prochazka
- Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
| | - Teresa Zulueta-Coarasa
- Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Ted Rogers Centre for Heart Research, University of Toronto, Toronto, Ontario, M5G 1M1, Canada
| | - Nika Shakiba
- Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
| | - Rodrigo Fernandez-Gonzalez
- Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Collaborative Program in Developmental Biology, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Ted Rogers Centre for Heart Research, University of Toronto, Toronto, Ontario, M5G 1M1, Canada
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, M5S 3G5, Canada
| | - Peter W Zandstra
- Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Collaborative Program in Developmental Biology, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, M5S 3ES, Canada
- Medicine by Design: A Canada First Research Excellence Fund Program, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
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Barr KA, Martinez C, Moran JR, Kim AR, Ramos AF, Reinitz J. Synthetic enhancer design by in silico compensatory evolution reveals flexibility and constraint in cis-regulation. BMC SYSTEMS BIOLOGY 2017; 11:116. [PMID: 29187214 PMCID: PMC5708098 DOI: 10.1186/s12918-017-0485-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 11/09/2017] [Indexed: 11/12/2022]
Abstract
BACKGROUND Models that incorporate specific chemical mechanisms have been successful in describing the activity of Drosophila developmental enhancers as a function of underlying transcription factor binding motifs. Despite this, the minimum set of mechanisms required to reconstruct an enhancer from its constituent parts is not known. Synthetic biology offers the potential to test the sufficiency of known mechanisms to describe the activity of enhancers, as well as to uncover constraints on the number, order, and spacing of motifs. RESULTS Using a functional model and in silico compensatory evolution, we generated putative synthetic even-skipped stripe 2 enhancers with varying degrees of similarity to the natural enhancer. These elements represent the evolutionary trajectories of the natural stripe 2 enhancer towards two synthetic enhancers designed ab initio. In the first trajectory, spatially regulated expression was maintained, even after more than a third of binding sites were lost. In the second, sequences with high similarity to the natural element did not drive expression, but a highly diverged sequence about half the length of the minimal stripe 2 enhancer drove ten times greater expression. Additionally, homotypic clusters of Zelda or Stat92E motifs, but not Bicoid, drove expression in developing embryos. CONCLUSIONS Here, we present a functional model of gene regulation to test the degree to which the known transcription factors and their interactions explain the activity of the Drosophila even-skipped stripe 2 enhancer. Initial success in the first trajectory showed that the gene regulation model explains much of the function of the stripe 2 enhancer. Cases where expression deviated from prediction indicates that undescribed factors likely act to modulate expression. We also showed that activation driven Bicoid and Hunchback is highly sensitive to spatial organization of binding motifs. In contrast, Zelda and Stat92E drive expression from simple homotypic clusters, suggesting that activation driven by these factors is less constrained. Collectively, the 40 sequences generated in this work provides a powerful training set for building future models of gene regulation.
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Affiliation(s)
- Kenneth A Barr
- Committee on Genetics, Genomics, and Systems Biology, University of Chicago, Zoology 111, 1101 E 57th St, Chicago, 60637, Illinois, USA.
- Department of Ecology and Evolution, The University of Chicago, Chicago, 60637, Illinois, USA.
| | - Carlos Martinez
- Department Biochemistry and Molecular Genetics, Northwestern University, Chicago, 60611, Illinois, USA
| | - Jennifer R Moran
- Department Human Genetics, The University of Chicago, Chicago, 60637, Illinois, USA
- Institute for Genomics & Systems Biology, The University of Chicago, Chicago, 60637, Illinois, USA
| | - Ah-Ram Kim
- School of Life Science, Handong Global University, Pohang, 37554, Gyeongbuk, South Korea
| | - Alexandre F Ramos
- Departamento de Radiologia - Faculdade de Medicina, Universidade de São Paulo & Instituto do Câncer do Estado de São Paulo, São Paulo, SP CEP, 05403-911, Brazil
- Escola de Artes, Ciências e Humanidades & Núcleo de Estudos Interdisciplinares em Sistemas Complexos, Universidade de São Paulo, Av. Arlindo Béttio, São Paulo, 1000 CEP 03828-000, SP, Brazil
| | - John Reinitz
- Committee on Genetics, Genomics, and Systems Biology, University of Chicago, Zoology 111, 1101 E 57th St, Chicago, 60637, Illinois, USA
- Department of Ecology and Evolution, The University of Chicago, Chicago, 60637, Illinois, USA
- Institute for Genomics & Systems Biology, The University of Chicago, Chicago, 60637, Illinois, USA
- Department Statistics, The University of Chicago, 5747 S. Ellis Avenue Jones 312, Chicago, 60637, IL, USA
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Bentovim L, Harden TT, DePace AH. Transcriptional precision and accuracy in development: from measurements to models and mechanisms. Development 2017; 144:3855-3866. [PMID: 29089359 PMCID: PMC5702068 DOI: 10.1242/dev.146563] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
During development, genes are transcribed at specific times, locations and levels. In recent years, the emergence of quantitative tools has significantly advanced our ability to measure transcription with high spatiotemporal resolution in vivo. Here, we highlight recent studies that have used these tools to characterize transcription during development, and discuss the mechanisms that contribute to the precision and accuracy of the timing, location and level of transcription. We attempt to disentangle the discrepancies in how physicists and biologists use the term ‘precision' to facilitate interactions using a common language. We also highlight selected examples in which the coupling of mathematical modeling with experimental approaches has provided important mechanistic insights, and call for a more expansive use of mathematical modeling to exploit the wealth of quantitative data and advance our understanding of animal transcription. Summary: This Review highlights how high-resolution quantitative tools and theoretical models have formed our current view of the mechanisms determining precision and accuracy in the timing, location and level of transcription in the Drosophila embryo.
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Affiliation(s)
- Lital Bentovim
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Timothy T Harden
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Angela H DePace
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
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Rothenberg EV. Fitting structure to function in gene regulatory networks. HISTORY AND PHILOSOPHY OF THE LIFE SCIENCES 2017; 39:37. [PMID: 29038942 PMCID: PMC5660880 DOI: 10.1007/s40656-017-0164-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Cascades of transcriptional regulation are the common source of the forward drive in all developmental systems. Increases in complexity and specificity of gene expression at successive stages are based on the collaboration of varied combinations of transcription factors already expressed in the cells to turn on new genes, and the logical relationships between the transcription factors acting and becoming newly expressed from stage to stage are best visualized as gene regulatory networks. However, gene regulatory networks used in different developmental contexts underlie processes that actually operate through different sets of rules, which affect the kinetics, synchronicity, and logical properties of individual network nodes. Contrasting early embryonic development in flies and sea urchins with adult mammalian hematopoietic development from stem cells, major differences are seen in transcription factor dosage dependence, the silencing or damping impacts of repression, and the impact of cellular regulatory history on the parts of the genome that are accessible to transcription factor action in a given cell type. These different features not only affect the kinds of models that can illuminate developmental mechanisms in the respective biological systems, but also reflect the evolutionary needs of these biological systems to optimize different aspects of development.
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Affiliation(s)
- Ellen V Rothenberg
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA.
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Fradin C. On the importance of protein diffusion in biological systems: The example of the Bicoid morphogen gradient. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:1676-1686. [PMID: 28919007 DOI: 10.1016/j.bbapap.2017.09.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 08/16/2017] [Accepted: 09/05/2017] [Indexed: 10/18/2022]
Abstract
Morphogens are proteins that form concentration gradients in embryos and developing tissues, where they act as postal codes, providing cells with positional information and allowing them to behave accordingly. Bicoid was the first discovered morphogen, and remains one of the most studied. It regulates segmentation in flies, forming a striking exponential gradient along the anterior-posterior axis of early Drosophila embryos, and activating the transcription of multiple target genes in a concentration-dependent manner. In this review, the work done by us and by others to characterize the mobility of Bicoid in D. melanogaster embryos is presented. The central role played by the diffusion of Bicoid in both the establishment of the gradient and the activation of target genes is discussed, and placed in the context of the need for these processes to be all at once rapid, precise and robust. The Bicoid system, and morphogen gradients in general, remain amongst the most amazing examples of the coexistence, often observed in living systems, of small-scale disorder and large-scale spatial order. This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman.
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Affiliation(s)
- Cécile Fradin
- Dept. of Physics and Astronomy, McMaster University, 1280 Main St W., Hamilton, ON L8S 4M1, Canada
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50
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Hannon CE, Blythe SA, Wieschaus EF. Concentration dependent chromatin states induced by the bicoid morphogen gradient. eLife 2017; 6:28275. [PMID: 28891464 PMCID: PMC5624782 DOI: 10.7554/elife.28275] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 09/08/2017] [Indexed: 12/29/2022] Open
Abstract
In Drosophila, graded expression of the maternal transcription factor Bicoid (Bcd) provides positional information to activate target genes at different positions along the anterior-posterior axis. We have measured the genome-wide binding profile of Bcd using ChIP-seq in embryos expressing single, uniform levels of Bcd protein, and grouped Bcd-bound targets into four classes based on occupancy at different concentrations. By measuring the biochemical affinity of target enhancers in these classes in vitro and genome-wide chromatin accessibility by ATAC-seq, we found that the occupancy of target sequences by Bcd is not primarily determined by Bcd binding sites, but by chromatin context. Bcd drives an open chromatin state at a subset of its targets. Our data support a model where Bcd influences chromatin structure to gain access to concentration-sensitive targets at high concentrations, while concentration-insensitive targets are found in more accessible chromatin and are bound at low concentrations. This may be a common property of developmental transcription factors that must gain early access to their target enhancers while the chromatin state of the genome is being remodeled during large-scale transitions in the gene regulatory landscape.
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Affiliation(s)
- Colleen E Hannon
- Department of Molecular Biology, Howard Hughes Medical Institute, Princeton University, Princeton, United States
| | - Shelby A Blythe
- Department of Molecular Biology, Howard Hughes Medical Institute, Princeton University, Princeton, United States
| | - Eric F Wieschaus
- Department of Molecular Biology, Howard Hughes Medical Institute, Princeton University, Princeton, United States
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